The present invention relates in general to a liquid metal cooled fast breeder reactor equipped with an improved fuel handling mechanism, and more particularly to an improved liquid metal cooled fast breeder reactor which permits a closer installation of a fuel handling mechanism relative to an upper reactor core structure, thereby establishing compactness of the total structure of the reactor.
In the conventional liquid metal cooled fast breeder reactors, whether loop-type or tank-type reactors, there is equipped, as shown in FIG. 1, a fuel handling mechanism 30 which comprises generally a fuel handling body 6 and a cylindrical housing 31 surrounding the fuel handling body for aseismatic purposes. More specifically, the conventional fuel handling mechanism 30 including the cylindrical housing 31 is provided at its lower end with a gripper 13 which is vertically moved by a gripper lifting device, and supported by a rotational driving device 16 and suspended therefrom within the reactor vessel 1 so that it is accessible to a selected one of core assemblies 9 in the reactor core 8. Thus, aseismatic supporting effects are achieved by the cylindrical housing 31, which embraces the suspended fuel handling body 6. In the case of a liquid metal cooled fast breeder reactor on a scale of 1,000 MWe, the housing 31 of its fuel handling mechanism will have approximately 10 m in length, 1.5 m in diameter and 10 ton in weight. From a viewpoint of achieving smaller and lighter structure of the reactor, it is necessary to decrease a diameter of a rotating plug 4 of the reactor vessel which supports both the fuel handling mechanism 30 and an upper reactor core structure 5 of the reactor. However, it is limited to place the fuel handling mechanism 30 closely adjacent to the upper core structure 5 due to the cylindrical housing 31, and the provision of the cylindrical housing is a bottleneck for producing smaller and lighter structure of the reactor. Besides, the housing 31 generally has a wall-thickness of about several tens of milimeters, and therefore repeatedly receives a thermal stress due to rocking motion of the liquid surface 12 of the liquid metal coolant in the reactor vessel 1 and the changes of operating temperature, and so forth. In order to decrease the thermal stress, it is necessary to provide, for example, a thermal insulator 32 on the external surface of the housing 31 adjacent to the liquid surface 12. This also have caused an increase of the weight of the housing and a difficulty in providing the fuel handling mechanism 30 in proximity to the upper core structure 5. The elements or parts represented by the other numerals in FIG. 1 will be explained hereinbelow in the description referring to FIG. 2 wherein like parts are identified by the same reference numerals in FIG. 1.